CARCINOGENESIS AND AGING .7. CARCINOGENIC EFFECT OF SINGLE TOTAL-BODY X-RAY-IRRADIATION IN YOUNG AND OLD FEMALE RATS

Female rats aged 3 and 14 months were exposed to single X-ray irradiation at a dose of 4 Gy. Total frequency of neoplasms and that of malignant tumors in the younger age group amounted to 78 or 42% and in the older age age group to 66 and 31% respectively, while in the corresponding age groups the figures were as follows: 48 or 7% (p < 0.05). The comparative analysis of the carcinogenic effect of irradiation in young and old rats has revealed that sensitivity of the mammaory gland epithelium, ovarian tissue and thyroid epithelium to malignant actions of irradiation decreases with age. The paramount importance in modification of tissue sensitivity to carcinogenic action of irradiation in aging is suggested to be related to age-dependent changes in the proliferative activity of the target tissues.